A novel multimode digital control approach for single-stage flyback power supplies with power factor correction and fast output voltage regulation

This paper describes a novel digital control approach to achieve the unity power factor and fast output voltage regulation for single-stage single-switch AC-DC flyback power supplies. This intelligent digital approach achieves the combined benefits of high performance, low cost and high reliability in a single controller. In this solution, the power converter is constructed with the simplest and least expensive basic flyback topology that does not require a bulk capacitor to store energy on its primary-side. The converter operates in various modes according to the line input voltage and the output load. For power factor correction, there are two operation modes: critical discontinuous conduction mode (CDCM) and discontinuous conduction mode (DCM). Two other operation modes apply to the output voltage regulation: fast transient mode during load transient and pulse frequency modulation (PFM) mode at light load. The IC incorporating these innovative solutions have been introduced by iWatt. In addition to describing this approach, this paper gives the experimental results obtained on a 90W (19.5 V 4.62 A) prototype